This project is designed to determine how 2 designated control gene loci (I and B1) of the fowl effect their changes during melanogenesis. This will be tested through analysis of heterokaryons of mutant melanocytes from cell cultures. A second objective is to determine whether these control loci affect neither, one, or both the structural pk and c loci. The first type of experiment will determine whether the two structural mutants complement as heterokaryons. They do complement "in vivo". The second type of experiment will determine whether the two control gene mutants exert their control through the cytoplasm, or whether their effects are nuclearly limited. This will be tested by forming heterokaryons between mutant and normal cells and comparing them to their respective heterozygote homokaryons. Depending on the results of the first two types of experiments, either type 3 or type 4 experiments will be performed. The type of experiment depends upon whether the nuclei of the heterokaryons show independent or cytoplasmically mediated control. Type 3 analysis will be performed when either integrated function of control genes and/or independent expression of structural genes makes heterokaryon analysis unnecessary or disadvantageous. Type 3 experiments will be ultrastructural and cytochemical investigations of diploid melanocytes of the I/I pk/pk, I/Ic/c, Bl/Blpk/pk, and Bl/Blc/c genotypes. It will be possible to distinguish between various control possibilities by comparing the hypertrophy of the Golgi systems. Type 4 analysis will be performed if the type 2 experiments indicate that either or both of the control gene mutations can exert their influence only through the nucleoplasm. Heterokaryon experiments will be designed so that complementation of structural mutations from the stocks described in the previous paragraph will indicate which control loci affect which structural loci. Six-day old cultures of melanocytes will be fused with lysolecithin and allowed to develop an additional 3-5 days. Cells of one parental type will be grown in H3-thymidine for identification. They will then be labeled with H3-dopa and the melanogenic organelles assayed autoradiographically for H3-dopa incorporation with the electron microscope.